In recent years, optical computing techniques have been developed for applications in the Oil and Gas Industry in the form of optical sensors on downhole or surface equipment to evaluate a variety of fluid properties. An optical computing device is a device configured to receive an input of electromagnetic radiation from a substance or sample of the substance and produce an output of electromagnetic radiation from a processing element, also referred to as an optical element. The optical element may be, for example, a narrow band optical element or an Integrated Computational Element (“ICE”) (also known as a Multivariate Optical Element (“MOE”).
Fundamentally, optical computing devices utilize optical elements to perform calculations, as opposed to the hardwired circuits of conventional electronic processors. When light from a light source interacts with a substance, unique physical and chemical information about the substance is encoded in the electromagnetic radiation that is reflected from, transmitted through, or radiated from the sample. Thus, the optical computing device, through use of the ICE core and one or more detectors, is capable of extracting the information of one or multiple characteristics/properties or analytes within a substance and converting that information into a detectable output signal reflecting the overall properties of a sample. Such characteristics may include, for example, the presence of certain elements, compositions, fluid phases, etc. existing within the substance.
Therefore, a need has arisen in the industry to develop ways in which to temporarily or permanently place optical computing devices in downhole tubing or piping. Such pipes and tubes are used for the production of reservoir fluids and can be in place for many years. As the well is produced, it is desired to know the composition of the fluids, as this knowledge is used in part to make decisions how to treat the fluids once they reach surface. However, there are considerations that dictate the configuration of sensors used in permanent placement applications. For example, the sensor needs to be robust and require little power, to allow it to be in place for many years. The sensors also need to be of sufficient size such that other tools and systems can be conveyed past the installed sensor along the tubing/pipe. Additionally, the sensors should minimally affect the flow of fluid in the tube. If the sensor affects the flow, there can be variations in the volumetric flow rate or pressure. These effects may lead to changes in the fluids composition. For example, solids entrained in the fluid may fall out and build up in low volumetric flow areas leading to eventual blockage. Alternatively, changes in pressure can cause dissolved gases to evolve from the fluid leading to inaccurate estimations of the fluids composition.
Moreover, traditional spectrometer instruments simply are not stable enough to withstand downhole conditions. Filter photometers are reasonably stable, but do not have the sensitivity to measure analytes of interest in complex oils. Additionally, many instruments cannot measure across large concentration ranges. For example, the water cut application requires a 0 to 100% water (or oil) coverage, and traditional instruments generally only detect a small fraction of this range . . . e.g. 0 to 10% or 70 to 80%. Finally, the sensors need to be low cost in order to place them along each collection tubular. So, for example, a single producing well might use up to 1,000 or more single sensors. If these cost ˜½ Million each as do some traditional sensors, this is clearly a large barrier to overcome.
Accordingly, the present invention meets these and other needs in the art through provision of cost-effective, robust, stabile, compact and power efficient implementations for optical computing devices as described herein.